Filter materials and filters made therefrom

ABSTRACT

The present invention relates to filter material for inclusion in a smoking article, wherein the filter material is in the form of a fibrous tow or a non-woven sheet comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 um. The invention also relates to processes for preparing filter material for inclusion in a smoking article, the filter material comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 μm. The invention further relates to filters or filter elements comprising the filter material, smoking articles comprising the same, and use of the filter material in smoke filtration.

FIELD

The present invention relates to filter materials for use in smoking articles. The invention also relates to filters or filter elements comprising the filter materials, smoking articles comprising the same, and use of the filter materials in smoke filtration.

BACKGROUND

A wide variety of fibrous materials have been suggested as filters for cigarette smoke. Cellulose acetate tow is the most commonly used filter material and the fibres generally have a mean diameter in the region of 20 μm.

SUMMARY

According to a first aspect of the invention, a filter material for inclusion in a smoking article is provided, wherein the filter material is in the form of a fibrous tow or a non-woven sheet comprising fine cellulose acetate fibres having a mean diameter of from about 1 μμm to about 15 μm.

In some embodiments, the tow or non-woven sheet is formed from fibres and at least about 80% by weight of the fibres are fine cellulose acetate fibres.

In some embodiments, the fine cellulose acetate fibres have a diameter of no less than 0.3 μm.

In some embodiments, the fine cellulose acetate fibres comprise cellulose acetate and an additive.

In some embodiments, the filter material further comprises a plasticizer which is one or more selected from the group consisting of: triacetin; polyethylene glycol; triethyl citrate; and triethylene glycol diacetate.

In some embodiments, the filter material removes from about 50% to about 90% phenol from tobacco smoke.

In some embodiments, the filter material removes from about 50% to about 90% cresol from tobacco smoke.

According to a second aspect of the invention, a process for preparing filter material for inclusion in a smoking article is provided, the filter material comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 μm, the process comprising electrospinning or centrifugal spinning or melt spinning.

In some embodiments, a cellulose acetate solution is spun, the solution having a cellulose acetate concentration of from about 6% to about 30%.

In some embodiments, the fine cellulose acetate fibres are produced by spinning through a spinneret using centrifugal force, and the spinneret spins at a rate of from about 4500 to about 7500 rpm.

In some embodiments, the flow rate of the cellulose acetate solution through the orifice(s) of the spinneret is from about 5 to about 100 ml/min.

In some embodiments, the fine cellulose acetate fibres are laid down as a non-woven sheet or non-woven web directly following spinning.

In some embodiments, the fine cellulose acetate fibres are drawn onto a base sheet upon which a non-woven sheet or web is formed by a vacuum pull, by air flow or by electrostatic charge.

According to a third aspect of the invention, a filter material is provided, obtained or obtainable by a process according to the second aspect.

According to a fourth aspect of the invention, a filter element or filter for a smoking article is provided, comprising a filter material according to the first aspect, or comprising a filter material obtained or obtainable by a process according to the second aspect.

In some embodiments, the filter has a pressure drop of from about 60 to about 140 mmWG.

In some embodiments, the filter comprises from about 30 to about 90 mg of filter material in the form of a fibrous tow or a non-woven sheet comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 μm.

In some embodiments, the filter comprises from about 40 to about 80 mg of said filter material.

According to a fifth aspect of the invention, smoking article is provided comprising a filter or filter element according to the fourth aspect.

According to a sixth aspect of the invention, there is provided use of the filter material according to the first or third aspect, in the filtration of tobacco smoke.

BRIEF DESCRIPTION OF THE FIGURES

In order that aspects of the invention may be more fully understood, embodiments thereof are described, by way of illustrative example, with reference to the accompanying drawing in which:

FIG. 1 is a schematic side view of a smoking article including a filter according to some embodiments.

DETAILED DESCRIPTION

Most commercial cigarette filters are made from cellulose acetate (CA) fibres or “tow”. This CA tow, which is used as cigarette filter material in many commercially available filter cigarettes, is referred to herein as “conventional” cellulose acetate. Conventional CA typically has a degree of substitution of less than 3.0, preferably in the range of 2.0 to 2.8, and most preferably in the range of 2.3 to 2.5.

The filaments of conventional CA tow have a diameter of approximately 20 μm. The filaments of conventionally used CA tow generally have a Y cross section, but it is known to make filaments with other cross-sectional shapes, including crenulated, X, and I (or “dog bone”).

The amount of filter tow in the filter rod (associated with a parameter called “tow weight”) determines the density of the filter rod. The firmness of the filter rod can be controlled by adding a so-called “plasticizer”, for example glycerol triacetate, usually referred to as triacetin. The plasticizer actually acts as a binder, binding adjacent fibres at their points of contact. This results in an increase in the hardness or structural rigidity of the rod formed from the tow.

Routinely measured filter parameters include pressure drop and ‘tar’ or NFDPM (nicotine-free dry particulate matter) and nicotine filtration efficiency and these parameters are related.

Pressure drop (also referred to as “draw resistance”) determines the amount of suction a smoker needs to apply to the cigarette to draw smoke through the filter. The pressure drop of the filter plus that of the tobacco column must be within a range acceptable to consumers, which is typically in the range 80-160 mm water gauge (WG). The pressure drop will be affected by the physical properties of the filter material, such as fibre diameter and cross-sectional shape. In addition, it will be affected by the manner in which the filter material is incorporated into the filter. For example, the packing is density of the filter material within the filter will affect the pressure drop.

Filtration efficiency refers to the proportion of the material retained by the filter compared with that entering it. The filtration efficiency is affected by the smoke flow velocity and is typically determined using a standard machine-smoking regime. The main purpose of a cigarette filter is to reduce the particulate smoke yield which is achieved by mechanical filtration of aerosol particles.

Herein, the filtration efficiency is measured for smoking by taking puffs of 35 ml volume and of a 2 second duration at 60 second intervals with the ventilation zone blocked.

Removal of specific constituents of the particulate phase is generally in proportion to the “tar” filtration efficiency. Gas phase smoke passes through cellulose acetate filters largely unaffected. Some semi-volatile constituents, e.g. phenolic species, can be selectively retained by conventional CA tow and this selective retention may be further enhanced by certain plasticizers. When used to filter cigarette smoke, conventional cellulose acetate tow has been shown to selectively remove phenol, cresol and pyridine.

The inventors have surprisingly found that the replacement of conventional cellulose acetate tow with cellulose acetate fibres having a smaller mean diameter results in greater than expected selective reduction from tobacco smoke of selected phenol compounds.

Therefore, in one aspect of the invention, a filter material for inclusion in a smoking article is provided, the filter material comprising cellulose acetate fibres having a mean diameter which is smaller than that of the fibres making up conventional CA tow.

The filter material may be in the form of a fibrous tow or a non-woven sheet, the tow or sheet comprising cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 μm. In some embodiments, the filter material is in the form of a fibrous tow or a non-woven sheet comprising fine cellulose acetate fibres.

As used herein, “fine fibres”, “fine cellulose acetate fibres” or “fine CA fibres” are cellulose acetate fibres having a mean diameter of from about 1 μm to about 15 μm, or from about 1 μm to about 10 μm, or from about 5 μm to about 10 μm, or from about 1 μm to about 7 μm.

In some embodiments, the mean is calculated based upon the number of fibres. In other embodiments, the mean is calculated based upon the mass of fibres.

In some embodiments, the filter material may preferably be in the form of a fibrous tow, the tow having an analogous structure to the conventional CA tow used in smoking article filters.

In some embodiments, the filter material is not a sheet formed by melt blowing in which fibres of relatively short length (for example, up to a maximum length of about 100 mm) are melt-bonded to form a web.

In some embodiments, the filter material, i.e. the tow or non-woven sheet, is formed from fibres and at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, at least about 99.5%, or at least about 99.8% by weight of the fibres are fine cellulose acetate fibres.

Alternatively or in addition, in some embodiments, the filter material may comprise at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, at least about 99.5%, or at least about 99.8% by volume fine fibres.

Alternatively or in addition, in some embodiments, the filter material may comprise at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99%, at least about 99.5%, or at least about 99.8% by surface area fine cellulose acetate fibres.

The tow or non-woven sheet may consist of the fine cellulose acetate fibres or may consist essentially of the fine cellulose acetate fibres.

In some embodiments, the tow or sheet is formed directly using the fine cellulose acetate fibres, without the need to first form the fine fibres into filaments, for example by spinning or a similar process. Thus, the tow or non-woven sheet is made up of individual fine fibres.

In some embodiments, individual fine fibres may have a sufficiently large diameter so that they do not dissolve when in use, for example when filtering tobacco smoke. In some embodiments, the fine cellulose acetate fibres have a diameter of no less than 0.3 μm.

Where the fine fibres are in the form of tow, the tow is made directly from the fibres of cellulose acetate, rather than being formed of filaments created from fine cellulose acetate fibres.

The fine cellulose acetate fibres comprise or consist of cellulose acetate. In some embodiments, the fibres comprise cellulose acetate and any additives or the like used in their manufacture and/or used in the manufacture of the filter material, such as a tow or non-woven sheet.

For example, in some embodiments, the fibres are formed from a cellulose acetate solution which may include an additive such as polyethylene oxide (PEO) which may act as a lubricant and/or may help to control the rate of evaporation of the solvent during the formation of the fibres. Some PEO may be present in the fine fibres produced in such as way. For the avoidance of doubt, PEO is an oligomer or polymer of ethylene oxide with a molecular mass greater than 20,000 g/mol or a molecular weight greater than 100,000.

In some embodiments, fine fibres include at least about 0.1%, at least about 0.5%, at least about 1%, at least about 2%, at least about 5%, at least about 10%, or at least about 15% of an additive by weight of the fine fibres. Additionally or alternatively, in some embodiments, the fine fibres include up to about 20%, up to about 15%, up to about 10%, up to about 5% or up to about 2% of an additive by weight of the fine fibres.

In some embodiments, the filter material includes at least about 0.1%, at least about 0.5%, at least about 1%, at least about 2%, at least about 5%, at least about 10%, or at least about 15% of an additive by weight of the filter material. Additionally or alternatively, in some embodiments, the filter material includes up to about 20%, up to about 15%, up to about 10%, up to about 5% or up to about 2% of an additive by weight of the filter material.

In some embodiments, the fine fibres may comprise at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99% by weight cellulose acetate.

After manufacture of the fine fibres, the filter material may be treated with other additives, such as plasticizers. Such additives which are added to the fibres will generally not be considered to form part of the fibres themselves.

In some embodiments, the plasticizer is one or more selected from the group consisting of: triacetin; polyethylene glycol (PEG); triethyl citrate (TEC); and triethylene glycol diacetate (TEGDA). For the avoidance of doubt, PEG is an oligomer or polymer of ethylene oxide with a molecular mass below than 20,000 g/mol or a molecular weight below than 100,000.

In some embodiments, the filter material includes at least about 0.1%, at least about 0.5%, at least about 1%, at least about 2%, at least about 5%, at least about 10%, or at least about 15% plasticizer by weight of the filter material. Additionally or alternatively, in some embodiments, the filter material includes up to about 20%, up to about 15%, up to about 10%, up to about 5% or up to about 2% plasticizer by weight of the filter material.

In some embodiments, the filter material may comprise at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, at least about 99% by weight cellulose acetate.

The filter material may have an acceptable and/or desirable filtration efficiency. The filter material may have an acceptable and/or desirable filtration efficiency for an aerosol such as tobacco smoke.

It has been found that the filter material according to the invention provides at least the same filtration efficiency per gram of filter material as conventional cellulose acetate tow. Indeed, in many embodiments, the filtration efficiency of the filter material of the invention is greater per gram of filter material than that of conventional cellulose acetate. This allows less filter material to be used whilst achieving the same filtration effect.

In some embodiments, an acceptable filtration efficiency for the filtration of tobacco smoke may be the removal of at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, or at least about 50% nicotine-free dry particulate matter (NFDPM). In some embodiments, an acceptable filtration efficiency for the filtration of tobacco smoke may be the removal of at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, or at least about 50% nicotine.

In some embodiments, the filter material of the invention removes at least about 60%, at least about 70%, at least about 75% or at least about 80% of the NFDPM. In some embodiments, the filter material of the invention removes at least about 60%, at least about 70%, at least about 75% or at least about 80% of the nicotine.

It has further been shown that the fine fibre cellulose acetate filter material exhibits increased phenol selectivity compared to conventional cellulose acetate tow.

In some embodiments, the filter material of the invention removes from about 50% to about 90% phenol from tobacco smoke. In some embodiments, the filter material of the invention removes from about 50% to about 90% cresol from tobacco smoke.

Thus, the filter material of the invention exhibits greater selectivity for phenol and cresol than conventional cellulose acetate tow (as shown in the Examples below).

The experimental data show that, by decreasing the diameter of the CA fibre, we get an improved filtration efficiency of the smoke particulate phase and an above expected increase in filtration efficiency of phenol and cresol.

Processes

In order to form fibres from cellulose acetate, the cellulose acetate may be dissolved in acetone to produce a solution which is then extruded by being forced out through one or more orifices to form fibres. Frequently, it will be desirable to filter the cellulose acetate solution before it is extruded.

Spinning is the basic technique used for forming fibres from substances in solution, such as cellulose acetate. The solution is generally forced through a cap or nozzle, called a spinneret. The spinneret is perforated with small holes and a filament is extruded through each one. A spinneret may have from one to several hundred or even thousand holes. As the filaments emerge from the holes in the spinneret, the liquid polymer is converted first to a rubbery state and then solidified. This process of extrusion and solidification of endless filaments is called spinning (however, it should not be confused with the process used to combine multiple fibres into a filament, which is also called spinning).

Solidification of the extruded polymer is achieved by evaporating the solvent in a stream of warm air or inert gas.

While extruded fibres are solidifying, or in some cases even after they have hardened, the filaments may be drawn to impart strength. Drawing pulls the molecular chains together and orients them along the fibre axis, creating considerably stronger fibres. This can also reduce the diameter of the fibres.

Following the exiting of the cellulose acetate from the spinneret, there may be rapid evaporation of the solvent from the surface of the extruded filament. This leads to the formation of a skin layer on the surface. As the solvent from within the body of the filament subsequently evaporates, the skin layer on the surface caves in, providing the fibre with a cross section having a collapsed shape.

The filter material of the invention is made by a spinning process. In such processes, various factors may be varied and/or controlled, for example the cellulose acetate concentration of the solution, the orifice size and/or the flow rate of the polymer solution through the spinneret, to provide fibres having a mean diameter of from about 1 μm to about 15 μm. In some embodiments, the fine cellulose acetate fibres formed by a spinning process have a mean diameter of from about 1 μm to about 15 μm, or from about 1 μm to about 10 μm, or from about 5 μm to about 10 μm, or from about 1 μm to about 7 μm. In some embodiments, the fine cellulose acetate fibres formed by a spinning process have a diameter of no less than 0.3 μm.

In some embodiments, the spinning is controlled to provide finer fibres than seen in conventional cellulose acetate tow. In some embodiments, this may be as a result of utilising electrostatic charge to draw out the fibres (electrospinning), or utilising high velocity air flow to blow the fibres, or by utilising centrifugal force to draw out the fibres from liquid feed stock (so-called forcespinning), or by melt spinning.

In some embodiments, it may be preferable to form the fine cellulose acetate fibres by a process comprising centrifugal spinning.

In embodiments where the fibres of cellulose acetate are produced by melt spinning, the cellulose acetate is heated to a temperature at which it has a desired viscosity for the process.

In some embodiments where the fibres of cellulose acetate are produced by other spinning processes, the fibres are made from a cellulose acetate solution. In some embodiments, the cellulose acetate solution, formed from cellulose acetate in acetone, has a cellulose acetate concentration of from about 6% to about 30%, from about 7% to about 25% or from about 8% to about 20%.

In some embodiments, the feedstock may be heated during spinning, for example to prevent gelling and the consequent clogging of the orifices that can be observed with some cellulose acetate solutions. For example, the temperature of the feedstock being spun may be from about room temperature (for example 20° C. or 25° C.) to about 60° C.

In embodiments where the fine fibre are produced by spinning using centrifugal force, the spinneret may spin at a rate of from about 4500 to about 7500 rpm, or from about 5000 to about 7000 rpm.

In some embodiments, the flow rate of the feedstock, i.e. of the cellulose acetate solution, through the orifice(s) of the spinneret is from about 5 to about 100 ml/min, or from about 10 to about 50 ml/min. In some embodiments, these flow rates may be used in combination with the spin rates mentioned above for centrifugal force spinning.

In some embodiments, the fine fibres are laid down as a non-woven sheet or non-woven web directly following spinning. In some embodiments, the fibres are drawn to a base sheet upon which the non-woven sheet is formed by a vacuum pull, by air flow or by electrostatic charge.

In some embodiments, the non-woven sheets have a basis weight or grammage of from about 5 to about 50 g/m² (also referred to as gsm), or from about 10 to about 40 g/m², or from about 15 to about 35 g/m².

In some embodiments, the non-woven sheets have a caliper of from about 100 to about 1500 μm, or from about 250 to about 750 μm.

In some embodiments, the fine cellulose acetate fibres of the present invention are not formed by a melt blowing process.

In some embodiments, the process comprises forming fine cellulose acetate fibres having a length of greater than 100 mm. These fibres may be used to form a fibrous tow or a non-woven sheet. In some embodiments the fibrous tow or non-woven sheet is subsequently cut to a desired size for inclusion in a filter or filter element.

Filters and Smoking Articles

The filter material may be incorporated into a smoking article, or a part thereof. In some embodiments, a filter or filter element containing the filter material is incorporated into a smoking article. The filter material, filter or filter element may be incorporated into a smoking article by any method known in the art.

As used herein, the term “smoking article” includes smokeable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes and also heat-not-burn products. In addition, in some embodiments, the term “smoking article”, as used herein, further encompasses aerosol generation devices, such as e-cigarettes and other nicotine inhalers, as well as inhalation devices such as so-called “heat-not-burn” devices in which tobacco is heated but not combusted.

Referring to FIG. 1, a smoking article 1 according to an embodiment of the invention comprises a filter 2 and a cylindrical rod of smokeable material 3, such as tobacco, aligned with the filter 2 such that one end of the smokeable material rod 3 abuts the end of the filter 2. The filter 2 is wrapped in a plug wrap (not shown) and the smokeable material rod 3 is joined to the filter 2 by tipping paper in a conventional manner. The filter 2 is substantially cylindrical and has a mouth end 4 and a smokeable material end 5. The filter 2 comprises filter material 6 as described herein.

Because of the enhanced filtration characteristics of the fine CA fibres, it is possible to achieve an equivalent or improved filtration compared to that of a conventional CA filter using less filter material. This means that less filter material needs to be used. In some embodiments, it may be desirable to make the filter to the same dimensions as used in a conventional cigarette design, namely having a target length of 144 mm and a target circumference of 24.3 mm. In other embodiments, the filters may be for use in smoking articles of other formats, such as so-called super-slim or demi-slim, the filters will have different dimensions.

When incorporated into a filter or filter element, the filter material may confer desirable physical properties. For example, pressure drop across the filter or filter element may be between 60 and 140 mmWG, which would be a desirable pressure drop when the filter or filter element is incorporated into a smoking article.

In some embodiments, a filter comprising the filter material of the invention may have a pressure drop of from about 60 to about 140 mmWG, from about 70 to about 130 mmWG, from about 75 to about 120 mmWG, from about 80 to about 110 mmWG, from about 85 to about 100 mmWG, or from about 90 to about 95 mmWG.

In some embodiments, a filter comprising the filter material of the invention may include filter material having a weight of from about 30 to about 90 mg, or from about 40 to about 80 mg. This is compared to a conventional cellulose acetate filter (of a so-called king-size format) in which approximately 120 to 130 mg of the cellulose acetate tow is included. For alternative filter formats, for example in those for use in a super-slim or demi-slim smoking article, the amount of filter material used would obviously be reduced.

In embodiments where less filter material of the invention is incorporated in a filter having conventional dimensions, this may mean that the filter is less densely packed with the filter material. In other embodiments, the filter may be designed so that the filter material is present in only part of the filter rod, for example in a central axial rod surrounded by a void or by other material. In such embodiments it may be desirable to ensure that the flow path of the mainstream smoke being drawn through the filter rod is channelled through the filter material. In alternative embodiments, the flow path may be variable. In an alternative approach, the filter may have one or more cavities. Such cavities may have essentially the same diameter as the filter material plug. For example, such a cavity may be formed between two plugs of filter material, or between one plug of filter material and the rod of smokeable material. In some embodiments, the cavity may house filter components such as adsorbent material, flavourants or additive release components.

In some embodiments, the filter material has an acceptable and/or desirable filtration efficiency and an acceptable and/or desirable pressure drop when in use, for example when the filter material is incorporated into a smoking article.

EXAMPLES

The fine fibre cellulose acetate filter materials used in the experiments of the examples set out below were produced by centrifugal spinning of a cellulose acetate solution. The concentration and the spinning of the spinneret were adjusted to obtain fibres of the desired mean diameter. The fibres were deposited on substrate sheet and removed to provide non-woven sheets of fine cellulose acetate fibres.

Example 1

Cellulose acetate tow was produced with an average fibre diameter of 2 μm. To test the filtration characteristics of a filter consisting of this material, test cigarettes were manufactured and compared to a control cigarette having a filter with filter material consisting of conventional cellulose acetate tow having a mean fibre diameter of about 20 μm.

The control cigarettes used were commercial Lucky Strike Blue cigarettes which had a filter made from cellulose acetate tow with a 20 μm mean fibre diameter and 7% triacetin as plasticiser. To prepare the test cigarettes, the filters of the Lucky Strike Blue cigarettes were removed and replaced with filter material consisting of unplasticised cellulose acetate filter tip having an average 2 μm fibre diameter.

Any filter tip ventilation was completely blocked on both cigarettes.

The filter of the test cigarettes was formed to provide a pressure drop which is equivalent to that of the control cigarettes.

As shown by the results set out in Table 1, at a matched pressure drop, although significantly less of the smaller diameter cellulose acetate filter material was used in the filters of the control cigarettes (30 mg cellulose acetate in the test cigarette compared to 124 mg in the control), the test cigarettes exhibited greater filtration efficiency. When the results are normalised to unit tar, there is enhanced reductions of phenol and cresol, even with the test cigarette filter material including no plasticiser. It is known that triacetin on cellulose acetate improves the selective filtration efficiency for phenol and cresol. The cigarettes were smoked under ISO smoking conditions.

TABLE 1 Filter Conventional CA 2 μm CA fibres Weight 124 mg 30 mg Pressure Drop 95 mmWG 90 mmWG Puff No. 6.1 5.9 NFDPM (mg/cig) 10 5.8 Nicotine 0.73 0.42 Water 5.5 1.2 CO 10.1 10.9 Hydroquinone 37.1 19.8 Resorcinol 3.1 1.9 Catechol 38.6 20.8 Phenol 11.5 4.1 m + p-Cresol 7.1 3.0 o-Cresol 3.0 1.1 NFDPM normalised Hydroquinone 3.71 3.41 Resorcinol 0.31 0.33 Catechol 3.86 3.59 Phenol 1.15 0.71 m + p-Cresol 0.71 0.52 o-Cresol 0.30 0.19 % Reduction Hydroquinone 8 Resorcinol −6 Catechol 7 Phenol 39 m + p-Cresol 27 o-Cresol 37

A negative % reduction means an increase in yield, whilst a positive % reduction means a decrease in yield.

Example 2

This experiment was carried out to investigate the effect of different fibre diameters of the cellulose acetate filter material.

To provide control cigarettes, filter tips were removed from a Lucky Strike Blue cigarette and replaced with a standard cellulose acetate filter tip with 20 μm fibre diameter (labelled CA 20 μm below). For the test cigarettes, filter tips were removed from a Lucky Strike Blue cigarette and replaced with: (i) a cellulose acetate filter tip with filter material consisting of fibre having an average diameter of 7 μm; (ii) a cellulose acetate filter tip with filter material consisting of fibre having an average diameter of 2 μm; and (iii) a cellulose acetate filter tip with filter material consisting of fibre having an average diameter of 0.8 μm.

Because of the small amount of the small diameter cellulose acetate required for filtration, this was incorporated into a narrow bore filter tube to get a better “fill” value.

This time no plasticiser was used on any filter and there was also no filter tip ventilation. The cigarettes were smoked under ISO smoking conditions.

Filtration efficiencies for the smoke particulate matter (NFDPM, nicotine, hydroquinone, resorcinol, catechol) are show in Table 2. The results demonstrate that the filtration efficiency increased using smaller diameter cellulose acetate fibres. Phenol and cresol filtration efficiencies are increased by a greater amount using the smaller diameter cellulose acetate fibres.

TABLE 2 Filter Empty 20 μm CA 0.8 μm CA 2 μm CA 7 μm CA tube fibres fibres fibres fibres Pressure Drop 95 90 93 97 mmWG mmWG mmWG mmWG CA Weight 124 11* 19* 46* (mg) Format KS KS Narrow Narrow Narrow bore bore bore Puff No. 6.1 6.1 6.9 6.2 6 NFDPM 19.5 10.9 7.7 5.9 6.3 (mg/cig) Nicotine 1.24 0.79 0.46 0.43 0.46 Water 5.9 1.9 1.9 1.3 1 CO 11 10.7 10.7 10.6 11.1 Hydroquinone 64.5 38.9 28.7 21.7 23.8 Resorcinol 4.9 3.1 2.2 1.7 1.9 Catechol 77.3 46.9 30.2 23.5 26.7 Phenol 54.0 22.4 10.4 3.9 5.6 m + p-Cresol 26.9 12.7 6.0 2.9 3.8 o-Cresol 12.4 5.7 2.5 1.1 1.5 NFDPM normalised Hydroquinone 3.31 3.57 3.73 3.67 3.78 Resorcinol 0.25 0.29 0.29 0.28 0.30 Catechol 3.96 4.30 3.92 3.98 4.24 Phenol 2.77 2.05 1.35 0.66 0.88 m + p-Cresol 1.38 1.16 0.78 0.49 0.60 o-Cresol 0.64 0.52 0.32 0.19 0.24 Filtration Efficiency (%) NFDPM 44 61 70 68 Nicotine 36 63 65 63 Hydroquinone 40 55 66 63 Resorcinol 36 54 65 61 Catechol 39 61 70 65 Phenol 59 81 93 90 m + p-Cresol 53 78 89 86 o-Cresol 54 80 91 88 Filtration Selectivity Nicotine 0.88 1.05 0.86 0.86 Hydroquinone 0.93 0.87 0.88 0.86 Resorcinol 0.88 0.85 0.86 0.82 Catechol 0.92 1.00 1.00 0.91 Phenol 1.36 2.05 4.28 3.20 m + p-Cresol 1.19 1.77 2.73 2.28 o-Cresol 1.22 1.95 3.33 2.67 *excluding tube CA

The selectivity data provided in Table 2 emphasises how good the fine fibres are at removing phenol. Selectivity is defined as the ratio of NFDPM filtration efficiency to smoke analyte filtration efficiency). A selectivity for a toxicant which is greater than 1 is an indication of selectivity and the higher the value, the greater the selectivity. Selectivity is desirable as it indicates that more toxicant is removed from the smoke than tar.

Example 3

The experiment was carried out to investigate the effect of the plasticizer and of the reduced diameter.

Control cigarettes were commercial Lucky Strike Blue cigarettes with filters comprising conventional plasticized cellulose acetate tow with a fibre diameter of about 20 μm (labelled CA+Pz below). For the test cigarettes, the filter tips were removed from a Lucky Strike Blue cigarette and replaced with: (i) unplasticised cellulose acetate tow with a fibre diameter of about 20 μm (labelled CA no Pz); and (ii) unplasticised cellulose acetate tow having an average fibre diameter of 9 μm (labelled 9 μm).

Any filter tip ventilation was completely blocked on all cigarettes. The Lucky Strike Blue control filter contained 7% triacetin which is known to give improved phenol and cresol reductions.

Filter tip pressure drops matched at approximately 85 mmWG. The small diameter cellulose acetate fibre filter tip weight was 91 mg, compared to the standard cellulose acetate weight of 125 mg. The cigarettes were smoked under ISO smoking conditions.

As before, for a matched pressure drop, less material with smaller diameter fibres is required. This also gives a higher filtration efficiency, as shown by the results set out in Table 3.

TABLE 3 Filter 20 μm CA no Pz 9 μm CA fibres 20 μm CA + Pz Puff No. 6.1 6.3 6.1 NFDPM (mg/cig) 10.9 7.7 10.4 Nicotine 0.79 0.55 0.70 Water 1.9 1.2 2.5 CO 10.7 10.7 11.5 Hydroquinone 38.9 32.5 47.1 Resorcinol 3.1 2.2 3.6 Catechol 46.9 32.5 47.1 Phenol 22.4 10.2 11.7 m + p-Cresol 12.7 6.3 7.0 o-Cresol 5.7 2.7 2.9 NFDPM normalised Hydroquinone 3.57 4.22 4.52 Resorcinol 0.29 0.29 0.34 Catechol 4.30 4.22 4.53 Phenol 2.05 1.33 1.12 m + p-Cresol 1.16 0.82 0.67 o-Cresol 0.52 0.35 0.28 % Difference in unplasticised samples Hydroquinone −18 Resorcinol −1 Catechol 2 Phenol 35 m + p-Cresol 30 o-Cresol 34

It can be seen that triacetin has a large effect on phenol and cresol filtration. However, for the unplasticised materials it still appears that the smaller diameter fibres give an enhanced phenol and cresol selectivity.

In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced and provide for superior filter materials. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. In addition, the disclosure includes other inventions not presently claimed, but which may be claimed in future. 

1. A filter material for inclusion in a smoking article, wherein the filter material is in the form of a fibrous tow comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 10 μm.
 2. A filter material as claimed in claim 1, wherein the tow is formed from fibres and at least about 80% by weight of the fibres are fine cellulose acetate fibres.
 3. A filter material as claimed in claim 1, wherein the fine cellulose acetate fibres have a diameter of no less than 0.3 μm.
 4. A filter material as claimed in claim 1, wherein the fine cellulose acetate fibres comprise cellulose acetate and an additive.
 5. A filter material as claimed in claim 1, wherein filter material further comprises a plasticizer which is one or more selected from the group consisting of: triacetin; polyethylene glycol; triethyl citrate; and triethylene glycol diacetate.
 6. A filter material as claimed in claim 1, wherein the filter material removes from about 50% to about 90% phenol from tobacco smoke.
 7. A filter material as claimed in claim 1, wherein the filter material removes from about 50% to about 90% cresol from tobacco smoke.
 8. A process for preparing filter material for inclusion in a smoking article, the filter material comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 10 μm, the process comprising electrospinning or centrifugal spinning or melt spinning.
 9. A process as claimed in claim 8, wherein a cellulose acetate solution is spun, the solution having a cellulose acetate concentration of from about 6% to about 30%.
 10. A process as claimed in claim 8, wherein the fine cellulose acetate fibres are produced by spinning through a spinneret using centrifugal force, and the spinneret spins at a rate of from about 4500 to about 7500 rpm.
 11. A process as claimed in claim 8, wherein the flow rate of the cellulose acetate solution through the orifice(s) of the spinneret is from about 5 to about 100 ml/min.
 12. A process as claimed in claim 8, wherein the fine cellulose acetate fibres are laid down as a non-woven sheet or non-woven web directly following spinning.
 13. A process as claimed in claim 12, wherein the fine cellulose acetate fibres are drawn onto a base sheet upon which a non-woven sheet or web is formed by a vacuum pull, by air flow or by electrostatic charge.
 14. A filter material obtained or obtainable by a process as claimed in claim
 8. 15. A filter element or filter for a smoking article, comprising a filter material as claimed in claim 1, or comprising a filter material obtained or obtainable by a process for preparing filter material for inclusion in a smoking article, the filter material comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 10 μm, the process comprising electrospinning or centrifugal spinning or melt spinning.
 16. A filter as claimed in claim 15, wherein the filter has a pressure drop of from about 60 to about 140 mmWG.
 17. A filter as claimed in claim 15 comprising from about 30 to about 90 mg of filter material in the form of a fibrous tow comprising fine cellulose acetate fibres having a mean diameter of from about 1 μm to about 10 μm.
 18. A filter as claimed in claim 17, comprising from about 40 to about 80 mg of said filter material.
 19. A smoking article comprising a filter or filter element as claimed in claim
 15. 20. A filter material as claimed in claim 1 configured for filtration of tobacco smoke. 